Water covers about 70% of the Earth’s surface yet we can’t get enough of it. As the world tackles with ways to efficiently utilize usable water sources, investors can use exchange traded funds to capitalize on the growing industry.

Over the next 40 years, water demand from power generation is expected to double globally, which would help demand for industrial water and wastewater solutions in the coming years, according to WaterWorld.

The World Energy Council estimates that total power demand for water is expected to rise 100 billion cubic meters by 2050.

For instance, Asia faces challenges to water supply for power generation to meet growing population and associated power requirements. China alone is projected to see water demand rise 15% in the next 40 years.

While the Earth is covered in water, 97% of all water is salt water, which leaves only 3% as useable fresh water and much of it is trapped as ice.

Looking at water consumption , about 70% of demand goes into irrigation and farming while industrial demand takes up 22% and domestic use makes up 8%.

Investors interested in the water industry can take a look at four ETF offerings.

The Guggenheim S&P Global Water Fund (NYSEArca: CGW) tacks companies associated with the global demand for water, including water utilities, infrastructure, equipment, instruments and materials. CGW has a 0.70% expense ratio.

The fund has 52 components and the top holdings include Pentair 7.6%, Geberit 5.8% and United Utilities group 5.8%.

Country allocations include U.S. 38.9%, U.K. 17.3%, Switzerland 8.1%, France 7.0%, Japan 5.3%, Hong Kong 4.4% Sweden 3.8%, Brazil 2.9%, Netherlands 2.6% and Israel 2.5%.

CGW is up 16.5% year-to-date.

The First Trust ISE Water ETF (NYSEArca: FIWtracks U.S. companies that derive their revenue from potable and wastewater industries.FIW has a 0.6% expense ratio.